There is an increasing interest in providing displays that are capable of reproducing realistic-looking images. One aspect of achieving realistic images is providing high peak luminance and high dynamic range. A typical natural scene includes areas that are very bright, for example the sun in the sky and highlights of brightly illuminated objects, as well as areas that are dim, for example objects in the shadows. Achieving realistic images of general scenes is not possible on displays that are incapable of high peak luminance.
Current projection technology does not scale efficiently to high luminance. For example, in many common projector designs, a light source, such as a xenon lamp, illuminates one or more spatial light modulators. The spatial light modulators direct some light to the screen while absorbing or redirecting other light. Achieving high luminance requires scaling up the power of the light source. The increasing power consumption of the light source becomes an obstacle to increasing the brightness of the light source to levels sufficient to provide peak luminance at a level typical of natural scenes. Moreover, a powerful light source can cause problems with overheating spatial light modulators and other components in the projector, among other issues.
As an example, a current digital cinema projector may have a light source that consumes 8 kilowatts of electrical power to illuminate a large screen producing a peak luminance of 48 nits (48 cd/m2). In order to achieve a peak luminance of 12,000 nits (a luminance commonly encountered in everyday life), the power of the light source would need to be scaled to over 2 megawatts. This is clearly impractical in most cases.
A further problem which prevents significant increases in the peak luminance of many conventional projection displays is that the contrast does not increase with peak luminance. In many such displays, increasing the intensity of the light source to achieve an increased peak luminance also raises the black level. Therefore, attempts to increase the peak luminance past a threshold will result in an unacceptably high black level.
A further obstacle to providing displays having high enough luminance to present realistic images is that the response of the human visual system to light is roughly logarithmic. By contrast, power requirements scale roughly linearly with luminance. Doubling the luminance of an image, assuming the same efficiency of the light source, requires doubling the power. However, doubling the luminance does not result in an image which will be perceived by a viewer as being twice as bright. Doubling the apparent brightness requires approximately squaring the luminance.
The foregoing examples of the related art and limitations related thereto are intended to be illustrative and not exclusive. Other limitations of the related art will become apparent to those of skill in the art upon a reading of the specification and a study of the drawings.